158 BELL SYSTEM TECHNICAL JOURNAL 



frequencies. From this divergence the absorption curve shown in 



Fig. 14 was obtained. Due to the relatively small angle subtended by 



the sound field of the horn at the higher frequencies, the indoor data 



where the condenser transmitter was rotated throughout a relatively 



large region in front of the horn, are not comparable with the outdoor 



data where the transmitter was located in one position on the horn 



axis. 



Conclusion 



From the above considerations it is obviously quite impossible to 

 interpret the significance of response measurements on loud speakers 

 in general unless such measurements are qualified by statements 

 regarding the acoustic measuring conditions. Especially must infor- 

 mation be given as to the position of the condenser transmitter relative 

 to the loud speaker when the measurements were made, the method of 

 measurement (pressure measured at one position or averaged within a 

 region), and the size and nature of the medium. In general response 

 measurements to be most indicative of the capabilities of the loud 

 speaker should be made with the condenser transmitter at a distance 

 from the loud speaker commensurate with or equivalent to the most 

 likely listening distance of an observer. 



To determine which of two loud speaker response-frequency charac- 

 teristics is the better involves in addition to the above discussed 

 acoustic considerations, an interpretation of the physiological signifi- 

 cance of the magnitude and position in the frequency spectrum of 

 departures in the curves from a straight horizontal line. Such an 

 interpretation involves many physiological factors, the discussion of 

 which is not within the scope of this paper. It should also be borne in 

 mind that the response-frequency characteristics described in this 

 paper are determined from steady state amplitude measurements and 

 that they therefore give little information as to transient or phase 

 distortion. However the cause of transient or phase distortion 

 (the storage and release of energy in the reactive elements of the loud 

 speaker) is also a cause of poor dynamical characteristics so that the 

 peaks and depressions in a response-frequency characteristic may also 

 be an indication of the phase and transient distortion. On the whole 

 the response-frequency characteristic even though complicated by 

 such a wide variety of factors has been found to be the most significant 

 single criterion upon which to base a judgement of the merits of a loud 

 speaker. 



